Conventionally, in order to achieve improved fuel economy of an internal combustion engine (referred to hereinafter as an ‘engine’), a valve opening/closing timing control device has come to be used that controls an opening/closing timing of one or both of an intake valve and an exhaust valve. This type of valve opening/closing timing control device controls the above opening/closing timing by changing a relative rotation phase of a drive-side rotary member that rotates synchronously with a crankshaft and a driven-side rotary member that rotates in unity with a camshaft.
Ordinarily, the optimal opening/closing timing of intake/exhaust valves differs depending on the running circumstances of the engine, such as when starting the engine or during vehicle running. When starting the engine, by constraining the relative rotation phase of the driven-side rotary member with respect to rotation of the drive-side rotary member (referred to hereinafter as the ‘relative rotation phase’) to a predetermined phase between a most retarded phase and a most advanced phase, an optimal opening/closing timing of the intake/exhaust valves for starting the engine is realized. However, during idling that follows engine start-up, if the relative rotation phase is maintained at the phase used when starting the engine, the amount of hydrocarbon (HC) emissions increases, so during idling that follows engine start-up, it is desirable to change the relative rotation phase to a phase that allows the amount of HC emissions to be suppressed. Also, when performing an idling stop in which the engine is temporarily stopped when the vehicle was stopped by stepping on a brake pedal during normal running, it is desirable to change to a relative rotation phase where the engine can be restarted easily while in a high-temperature state. Related technology is disclosed in Patent Document 1 cited below.
Patent Document 1 discloses a variable valve timing control device of an internal combustion engine provided with a function to lock at an intermediate locked phase, where a rotation phase of a camshaft with respect to a crankshaft of an internal combustion engine is positioned in approximately the middle of an adjustable range of that rotation phase. This variable valve timing control device of an internal combustion engine is configured having a lock control means that controls a hydraulic control device so as to lock the rotation phase of the camshaft at the intermediate locked phase with a lock pin when a lock request has occurred. When a lock request has occurred, the lock control means controls the hydraulic control device such that the rotation phase of the camshaft moves past the intermediate locked phase while the lock pin is biased in a locking direction. During this phase variation control, when the rotation phase of the camshaft has become unable to move near the intermediate locked phase, the lock control means further changes a control amount of the hydraulic control device by a predetermined amount in a direction to move the rotation phase of the camshaft. At this time, locking is determined to be complete in a case where the rotation phase of the camshaft does not move.